Several possibilities for connecting the shaft of a drive unit with the shaft of an rotary encoder are known. For example, the connection can be established with the aid of suitable couplings, perhaps such as those described on page 41 of "Digital Longitudinal and Angular Metrology" by A. Ernst, Verlag Moderne Industrie, publs., 3rd ed., 1989. With extreme measuring demands, correspondingly high demands are also made regarding the torsional rigidity on such couplings. An alternative for avoiding the problems arising in this connection lies in the use of a so-called stator coupling where the actual coupling is not disposed on the rotor side but rather is disposed between the drive housing and the scanning unit of the rotary encoder, i.e. on the stator side. Such a coupling is known, for example, from FIG. 24 on page 43 of the above mentioned book.
In the case of stator coupling of the drive and rotary encoder shafts, the driveshaft is rigidly connected with the rotary encoder shaft by the aid of a center screw which is arranged coaxially with respect to both shafts. However, problems arise under certain conditions with this type of rotary encoder mounting. For example, the place where the two shafts meet each other may not directly accessible. If at the same time a defined angular orientation between the two shafts is demanded, for example, because of the defined association of a reference pulse of the rotary encoder to the driveshaft, an elaborate adjusting process of the two systems with respect to each other is the result. There is furthermore the danger that, following the performance of an adjustment of the two shafts with respect to each other, the two shafts are again twisted with respect to each other in an undesirable way because of the tightening of the central screw.